Oh wow. I don't know what store you went to, but that rep does not know what he's talking about. Go to a corporate store, and they will exchange the phone if it is behaving badly. Sounds like you have a faulty device.
But I don't know how long you've been having this problem, so I am not even sure if that is still adb option for you since out sounds like you're not exactly the happiest camper at the moment. You cam also of course try a factory reset and see what happens, but I'm not holding my breath.
Why didn't you start a thread here earlier about you're problems? I'm sure you'd have gotten those advices before things got unbearable. If you are trying to sell it, yeah, craigslist is your best bet that I know of... Or try making a price here. You never know, one of the forum readers might take you up on that offer. Just start a thread about it.
Good luck, bro.